GLOSSARY. 283 



Metamorphosis. Changes undergone by the individual before at- 

 taining the perfect state. 



Metapodium. The posterior part of the foot in the Mollusca. 



Metapophyses. Lateral processes of the vertebrae. 



Metasternum. The under part of the metathorax of an insect. 



Metasthenic. Having the maximum power in the posterior ex- 

 tremities. 



Metastoma. The labium so-called of a Crustacean. 



Metatarsus. The assemblage of bones between the tarsus and the 

 toes. 



Metathorax. The third or posterior segment of the thorax in 

 insects. 



Microbia. Extremely minute life-producing organisms in the air. 



Micropyle. An aperture in the ovum through which the male 

 element enters. 



Mimetic. When animals of different groups resemble one 

 another. 



Mimicry or imitation. A repetition of form and colour. In 

 many cases it has been shown by Mr. Bates, who first called 

 attention to this subject, that this superficial resemblance acts 

 as a safeguard to the form most exposed to attack. Mr. 

 Darwin thinks it is " only explicable on the theory of descent;" 

 but this does not explain the resemblance of many insects to 

 leaves and twigs of trees, sometimes as if covered with moss, 

 or of others to the excreta of birds, &c. 



Miocene. The middle Tertiary epoch. 



Molecule. " The smallest possible portion of a particular sub- 

 stance" ( Clerk-Maxwell). "Every atom is a molecule, but every 

 molecule is not an atom." 



Monadiary. The common envelope of a monad assemblage. 



Monaxial. When the axis is in one direction only. 



Monism. The descent of all organic beings from one primitive 

 stock. 



Monistic theory holds that creation was the product of natural 

 forces. 



Monoecious. When the male and female are associated in one 

 organism. 



Monomyary. When a bivalve shell has only a single muscle. 



Monophyletic. Derived from a single form. 



